x86, kdump, ioapic: Reset remote-IRR in clear_IO_APIC

In the kdump scenario mentioned below, we can have a case where
the device using level triggered interrupt will not generate any
interrupts in the kdump kernel.

1. IO-APIC sends a level triggered interrupt to the CPU's local APIC.

2. Kernel crashed before the CPU services this interrupt, leaving
   the remote-IRR in the IO-APIC set.

3. kdump kernel boot sequence does clear_IO_APIC() as part of IO-APIC
   initialization. But this fails to reset remote-IRR bit of the
   IO-APIC RTE as the remote-IRR bit is read-only.

4. Device using that level triggered entry can't generate any
   more interrupts because of the remote-IRR bit.

In clear_IO_APIC_pin(), check if the remote-IRR bit is set and if
so do an explicit attempt to clear it (by doing EOI write on
modern io-apic's and changing trigger mode to edge/level on
older io-apic's). Also before doing the explicit EOI to the
io-apic, ensure that the trigger mode is indeed set to level.
This will enable the explicit EOI to the io-apic to reset the
remote-IRR bit.

Tested-by: Leonardo Chiquitto <[email protected]>
Signed-off-by: Suresh Siddha <[email protected]>
Fixes: https://bugzilla.novell.com/show_bug.cgi?id=701686
Cc: Rafael Wysocki <[email protected]>
Cc: Maciej W. Rozycki <[email protected]>
Cc: Thomas Renninger <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions